Generally, as shown in FIG. 1, a telephone 10 is connected via a telephone loop 12 to the line side 14 of a central office switch 16. This connection enables a user of the telephone 10 to communicate with others, either on the line side 14, or on the trunk side 18, which connects the central office switch 16 to other central offices via central office trunks. The telephone loop 12 typically consists of two conductors commonly referred to as the "tip" 20 and "ring" 22, which enable a user of the telephone 10 to talk and listen at the same time. The central office switch 16 includes switching fabric 15, to direct calls between the line side 14 and trunk side 18, or between two lines on the line side 18. The central office switch's 16 directing of calls is controlled by processors 17.
Conventional call waiting service occurs when a subscriber of such a service is engaged in a voice call with a second party and a third party calls the subscriber, seeking to speak with the subscriber. In this circumstance, conventional call waiting service interrupts the subscriber's second party call with a brief audible call waiting tone, typically 440 hz for 300 milliseconds. For example, the subscriber's line is interrupted 300 milliseconds with a 440 hz tone. As a result, the subscriber is notified of the third party's call without appreciable disruption to the subscriber's second party call. The third party, unaware that the subscriber is engaged in a telephone call with the second party, hears audible ringing.
A conventional call waiting service also provides a subscriber the option to either "take" the third party call and place the second party call "on hold" or continue the second party call and ignore the third party call. For example, a subscriber can elect to "take" a third party call by flashing the switch hook on the subscriber's telephone, which results in the second party call being placed on "hold" and the subscriber's telephone connection being switched to the third party call. If the subscriber elects to continue the second party call, the third party continues to hear an audible ring or is given a busy signal or is switched to the subscriber's voice messaging service.
Traditionally, telephone lines are used for voice calls between persons. However, telephone lines are increasingly used for data calls, i.e., data transmissions and communications between machines including, for example, facsimile machines and computers. Typically, telephone lines solely dedicated to data calls are provided in addition to telephone lines solely dedicated to voice calls. Recently, data calls have become an increasingly affordable and popular means of communication, especially at home where usually a single telephone line is provided. For example, the use of a telephone line, with a computer, to navigate the Internet has become an increasingly popular at-home activity. In this regard, a subscriber uses a computer to communicate with a remote computer system via a telephone line, which maybe the same telephone line ordinarily used for voice calls.
The interruption caused by conventional call waiting service, e.g. 440 hz for 300 milliseconds, is often incompatible with a subscriber's data call. In this regard, a computer communicates with a remote computer system via telephone line by the use of a modem. The modem is a device which converts a digital signal from the computer into an analog signal for transmission via the telephone line, and converts an analog signal from the telephone line into a digital signal for receipt by the computer during the data conversion process. The modem typically detects a carrier signal, which is a signal sent by the remote computer system containing information. A conventional call waiting tone may interrupt a continuous carrier signal, thereby causing the loss of the carrier signal and appreciable disruption of the data call.
Moreover, a subscriber, realizing that their data call may be interrupted, may deactivate the conventional call waiting service during the subscriber's data call. Consequently, the subscriber will not be notified of third party calls during the data call, thereby defeating the purpose of a conventional call waiting service.